Optical Coherence Tomography (OCT) is a technique for performing high-resolution cross-sectional imaging that can provide images of tissue structure on the micron scale in situ and in real time [Huang et al. (1991)]. OCT is a method of interferometry that determines the scattering profile of a sample along the OCT beam. Each scattering profile is called an axial scan, or A-scan. Cross-sectional images, and by extension 3D volumes, are built up from many A-scans, with the OCT beam moved to a set of transverse locations on the sample. Motion of the sample with respect to the OCT scanner will cause the actual locations measured on the sample to be arranged differently than the scan pattern in scanner coordinates, unless the motion is detected and the OCT beam placement corrected to track the motion.
In recent years, frequency domain OCT techniques have been applied to living samples [Nassif et al. (2004)]. The frequency domain techniques have significant advantages in speed and signal-to-noise ratio as compared to time domain OCT [Leitgeb, R. A., et al., (2003); de Boer, J. F. et al., (2003); Choma, M. A., et al. (2003)]. The greater speed of modern OCT systems allows the acquisition of larger data sets, including 3D volume images of human tissue.
In the case of ophthalmology, a typical patient can comfortably hold his eye open for a few seconds. OCT systems can advantageously use these few seconds to collect extensive images. During such an acquisition, motion of the patients head and natural shifts in the patient's fixation will distort the image. Tracking the motion of the eye to correct the placement of the OCT beam has proven useful [U.S. Pat. No. 6,736,508; Hammer, D. X., et al. (2005)]. There is also motion along the OCT beam, which is not detectable by the common designs of eye trackers, but which does distort the OCT image.
There is therefore a need for a method to correct the placement of OCT image data acquired on a moving sample. The correction could be applied to the mechanism scanning the OCT beam, to approximately follow the motion of the sample. Alternatively, the correction could be applied when images are built from the A-scans acquired in the presence of sample motion. The need is for a method to determine the motion, in three dimensions, of the sample during the acquisition of the A-scans. A method that does not require an additional optical system for eye tracking would have the advantages of simplicity and lower cost.